A typical gas turbine engine includes a power section, a gear box, and various accessories such as a starter, fuel control, etc. The power section includes a compressor, a turbine, and a combustor. The compressor and turbine sections of the engine can rotate at speeds as high as 100,000 rpms. Air is compressed in the compressor to several atmospheres, for example, before it goes to the combustor. The combustor is split into two zones. At full load, the primary combustion chamber operates at fairly close to stoichiometric, the ideal fuel/air ratio. All of the fuel, and approximately 1/4 of the air or less, start to burn in this zone. The remainder of the air enters the secondary combustion zone through holes in the burner liner. This air provides a relatively cool blanket between the burning gases and the liner before it mixes. This serves to keep the liner cool. It also dilutes the temperature of the hot gases down to the point where the turbine nozzles and wheels will have a long life.
Accordingly, in the combustor, the fuel is burned, which heats the air, which then expands through the turbine wheels. The turbine wheels drive the compressors and, through the reduction gear box, the generator.
It is sometimes desirable to use natural gas rather than diesel fuel in a gas turbine engine because natural gas is generally less expensive, requires no storage tank, burns cleaner, produces significantly less NO.sub.x and provides higher efficiency and more power than diesel fuel.
A major problem with the use of natural gas is that it must be compressed enough to enter the combustor, and known gas compressors are very expensive and require significant energy to run. Most of the compressors available are screw-type or reciprocating compressors. They are generally equipped with gas coolers, oil separators, and accumulators.
Due to the high cost of add-on gas compressors, it is desirable to provide a method and apparatus for compressing the gas in a manner which eliminates the add-on gas compressor, while maintaining the required concentration of natural gas in the mixture which is injected into the primary zone of the combustor.